Global impact of the Antarctic ozone hole: Chemical propagation

Abstract

A model is presented for the chemical mixing of stratospheric air over spatial scales from tens of kilometers to meters. Photochemistry, molecular diffusion, and strain (the stretching of air parcels due to wind shear) are combined into a single one‐dimensional model. The model is applied to the case in which chemically perturbed air parcels from the Antarctic stratosphere are transported to mid‐latitudes and strained into thin ribbon‐like filaments until they are diffusively mixed with the ambient stratosphere. We find that the parcels may be treated as evolving in chemical isolation until the final mixing. When parcels reach a transverse thickness of 50–100 m in the lower stratosphere, they are rapidly dispersed by the combination of molecular diffusion and strain. The rapidity of the final mixing implies a lower limit to the vertical scales of inhomogeneities observed in the lower stratosphere. For this sensitivity study we consider four types of Antarctic air: a control case representing unprocessed polar air; heterogeneous processing by polar stratospheric clouds (PSCs) that has repartitioned the Clx and NOy families; processing that also includes denitrification and dehydration; and all processing plus 90% ozone depletion. Large abundances of ClO, resulting initially from heterogeneous processing of stratospheric air on PSCs, are sustained by extensive denitrification. (One exception is the case of Antarctic air with major ozone depletion in which ClO is converted rapidly to HCl upon release of small amounts of NOx as a result of the extremely nonlinear Clx‐NOy chemical system.) ClO concentrations in the mid‐latitude stratosphere should be enhanced by as much as a factor of 5 due to the mixing of air processed around the Antarctic vortex and will remain elevated for most of the following season. Chemical propagation of the Antarctic ozone hole occurs in two phases: rapid loss of ozone in the heterogeneously processed parcels as they evolve in isolation, and more slowly, a relative recovery of ozone over the following months. Another important effect is the transport of denitrified Antarctic air reducing NOx and hence the total catalytic destruction of ozone throughout the southern mid‐latitudes. In Antarctic air that has already been depleted of ozone within the vortex, little additional loss occurs during transport, and the propagation of chemically perturbed air acts partially to offset the deficit at mid‐latitudes caused by dynamical dilution of the ozone hole. In air which has not experienced substantial ozone loss, chemical propagation can generate a net ozone deficit of order 2–3% at mid‐latitudes.

Seasonal and interannual variability of the budgets of N2O and CCl3F

“…The chemistry of N20 and CC13F is parameterized by their zonally and monthly averaged loss frequencies. These parameters are calculated from a photochemical box model using observed climatic values for temperature, ozone, and other trace gases [Availone and Prather, 1997;Prather and Jaffe, 1990]. Parameterized convection and the associated horizontal diffusion occur in the troposphere, but not in the stratosphere.…”

Impact of rocket exhaust plumes on atmospheric composition and climate ― an overview

“…Averaged over the years 2000 to 2002, the total rocket propellant emission from a §eet of space shuttles, Titan IV, Proton, Long March, Ariane 5, Soyuz, Zenit, and smaller rocket launch vehicles has been calculated to amount to ∼ 30 Gg per year of which about 9 Gg per year are emitted into the stratosphere [13]. While the total amount of rocket emissions into the stratosphere is of similar magnitude as the meteoric in §ux, the particulate alumina fraction of the rocket emissions in stratosphere is about one third of the total emissions and amounts to ∼ 3 Gg annually.…”

“…Two-(2D) and three-dimensional (3D) atmospheric chemistry transport models (CTM) were used to follow the buildup of exhaust products and their perturbation to stratospheric ozone levels [10]. These models include the 2D chemistry AER model [11], the GSFC model [12], and the 3D GISS model for chemical tracers [13]. The three CTM derived chlorine enhancements of less than 0.6% above the background due to emissions from a §eet of 9 space shuttles and 3 Titan rockets representative for the 1990 §eet [10].…”

Retrieving the vertical distribution of stratospheric OClO from Odin/OSIRIS limb-scattered sunlight measurements

“…The O 3 mean state distribution is taken from the four-dimensional climatology of Li and Shine (1995) which is based on satellite and ozonesonde data sets. The NO 2 information is taken from a climatology constructed using the PRATMO photochemical box model (Prather and Jaffe, 1990;McLinden et al, 2000) that accounts for the diurnal variation of this species. The OClO a priori distribution is described in Sect.…”